Recently, rapid progress has been made in reducing the weight, decreasing the thickness, and reducing the size of electric and electronic instruments, and there is a strong demand for a reduction of the weight, a decrease in thickness, and a reduction in size of various electromagnetic material elements used for these instruments. In this connection, a development of novel materials having further improved properties is also strongly demanded.
New electroconductive materials have been widely developed to satisfy these demands. For example, since polyacetylene is given an electroconductivity as high as 10.sup.2 to 10.sup.3 s/cm by doping with iodine or arsenic pentafluoride [see Synthetic Metals, Volume 1, No. 2, page 101 (1979/1980)] and has excellent charge-discharge characteristics, polyacetylene has been investigated as an electrode material of a secondary battery. Moreover, since polyacetylene has absorption characteristics such that beams to be absorbed are close to solar beams, polyacetylene is under examination as a material of a solar cell.
However, polyacetylene is easily oxidized and doped polyacetylene is very sensitive to moisture. Moreover, arsenic pentafluoride or the like used for manifesting a high electroconductivity is highly toxic and is dangerous to the human body.
Polythiophene is under examination as an electroconductive material or battery electrode material because it has a conjugated structure similar to that of cis-type polyacetylene, and a peculiar electron structure containing sulfur atoms. Moreover, polythiophene is under investigation as an electrochromic material in which the color is changed by doping. For example, A. M. Druy et al reports that if 2,2'-bithienyl is electrochemically polymerized, a color change of blue-red is caused in the formed polymer in the oxidized state-reduced state and this change is reversible, and the polymer is valuable as an electrochromic material [J. de. Physique, 44, 6, C3-595 (1983)].
However, polythiophene has a problem in that since polythiophene is unstable in the doped state and is easily dedoped, it is difficult to maintain a high electroconductivity.
In view of the foregoing defects of the conventional techniques, it is a primary object of the present invention to provide a novel polymer which is very stable in air and can be easily doped with an ordinary dopant so that it is possible to maintain a high electroconductivity.